271 Analog MUX module
271 : Analog MUX module
- Author: Pat Deegan
- Description: Pipe 4 or 8 analog signals around through switchable passgates, useful for adding debug and inspection to analog projects without wasting many pins
- GitHub repository
- Clock: 0 Hz
How it works
This is a package that gives two different mulitplexers a spin. The core is a set of 4 passgates (letting signals pass between A and Z sides) which are "one-hot", so one of them is enabled at a time. If you tie all the Zs together, you have a simple 4:1 mux. The 8 passgate version is an extension of this, and it may be used as 8 analog switches (only one on at a time) or an 8:1 mux.
In order to give it a good run, numerous test scenarios were implemented that allow charactirizing the passgates themselves, as well as chaining the muxes together.
This system has, in addition to the muxes, a ring oscillator and driver (created by Matt Venn), a manually laid out digital block to convert bits to the one-hot signals needed to control the passgates, and an openlane generate simple counter, that is clocked directly from the ring oscillator, such that we can drive it at hundreds of megahertz, divide down the clocking and shoot it through the mux over an analog pin.
How to test
Watch my video.
External hardware
Analog stuff.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | RSEL0 | ||
| 1 | RSEL1 | ||
| 2 | RSEL2 | ||
| 3 | SEL0 | ||
| 4 | SEL1 | ||
| 5 | enable_counter | ||
| 6 | enable_ringosc | ||
| 7 |
Analog pins
ua | PCB Pin | Internal index | Description |
|---|---|---|---|
| 0 | B4 | 10 | VRES |
| 1 | B1 | 7 | RINGOUT |
| 2 | B3 | 9 | MUXOUT |
| 3 | B2 | 8 | LADDEROUT |